8.Property, Plant and Equipment, Net


As at December 31	2017						2016
		Cost		Accumulated DD&A		Net		Cost		Accumulated DD&A		Net

Canadian Operations
Proved properties	$	14,555	$	(14,047)	$	508	$	13,159	$	(12,896)	$	263
Unproved properties		311		-		311		285		-		285
Other		43		-		43		54		-		54
		14,909		(14,047)		862		13,498		(12,896)		602

USA Operations
Proved properties		25,610		(23,240)		2,370		26,393		(25,300)		1,093
Unproved properties		4,169		-		4,169		4,913		-		4,913
Other		16		-		16		44		-		44
		29,795		(23,240)		6,555		31,350		(25,300)		6,050

Market Optimization		7		(5)		2		6		(4)		2
Corporate & Other		2,299		(764)		1,535		2,148		(663)		1,485
	$	47,010	$	(38,056)	$	8,954	$	47,002	$	(38,863)	$	8,139

Canadian and USA Operations property, plant and equipment include internal costs directly related to exploration, development and construction activities of $208 million, which have been capitalized during the year ended December 31, 2017 (2016 - $161 million). Included in Corporate and Other are $63 million (2016 - $58 million) of international property costs, which have been fully impaired.

For the year ended December 31, 2017, the Company did not recognize any ceiling test impairments in the Canadian or U.S. cost centres. For the year ended December 31, 2016, the Company recognized before-tax ceiling test impairments of $493 million (2015 - nil) in the Canadian cost centre and $903 million (2015 - $6,473 million) in the U.S. cost centre. The impairments recognized in 2016 are included with accumulated DD&A in the table above and resulted primarily from the decline in the 12-month average trailing prices which reduced proved reserves volumes and values.

The 12-month average trailing prices used in the ceiling test calculations reflect benchmark prices adjusted for basis differentials to determine local reference prices, transportation costs and tariffs, heat content and quality. The benchmark prices are disclosed in Note 25.

Capital Lease Arrangements

The Company has several lease arrangements that are accounted for as capital leases including an office building and an offshore production platform.

As at December 31, 2017, the total carrying value of assets under capital lease was $46 million (2016 - $51 million), net of accumulated amortization of $684 million (2016 - $648 million). Liabilities for the capital lease arrangements are included in other liabilities and provisions in the Consolidated Balance Sheet and are disclosed in Note 13.

Other Arrangement

As at December 31, 2017, Corporate and Other property, plant and equipment and total assets include a carrying value of $1,255 million (2016 - $1,194 million) related to The Bow office building, which is under a 25-year lease agreement. The Bow asset is being depreciated over the 60-year estimated life of the building. At the conclusion of the 25-year term, the remaining asset and corresponding liability are expected to be derecognized as disclosed in Note 13.